Saving/Exporting an Image (Directly from 3D View)
Your only options are to either do an OpenGL Render (available via the Render menu at the top of the window) - which will re-render your image using OpenGL (which is what the viewport uses so is quick and should look the same as your image) - or you can tell Blender to take a screenshot of your current Blender window by pressing Ctrl+F3 (although once you've saved your screenshot you'll need to open an image editor (eg, Gimp) to trim off the rest of the window as the screenshot will consist of everything).